Booster brake mechanism



March 17, 1959 D. T. AYERS, JR

BOOSTERBRAKE MECHANISM 3 Sheets-Sheet 1 Filed Feb. 15, 1955 INVENTOR 0Av/o TA YEES, Je.

BY V. ATTORNEY March 17,1959 D. T. AYERS, JR

' BOOSTER BRAKE MECHANISM 3 Sheets-Sheet 2 Filed Feb. l5. 1955 7ZNVENTOR DA |//0 77A YE/ES Je.

ATTORNEY March 17, 1959 D. T. AYERS, JR

BOOSTER BRAKE MECHANISM 5 Sheets-Sheet 3 Filed Feb. 15, 1955 INVENTOR 0AW0 7/) YER 5 JE.

0*; BY ATTORNEY nited States Patent BOOSTER BRAKE MECHANISM David T.Ayers, Jr., Birmingham, Mich., assignor to Kelsey-Hayes Company, acorporation of Delaware Application February 15, 1955, Serial No.488,185

Claims. (Cl. 188-152) This invention relates to a booster brakemechanism and is an improvement over the structures disclosed in thecopending applications of Jeannot G. Ingres, Serial No. 463,492, filedOctober 20, 1954, and Serial No. 488,258, filed February 15, 1955.

In the first-mentioned copending application referred to above, there isshown a bellows type motor for applying power to assist the operator inefiecting movement of the master cylinder piston. A lever mechanism isemployed comprising a pedal lever and a power lever, and unlike priorconstructions, the power lever rather than the pedal lever is pivotedfor turning movement on a fixed axis. The pedal lever is pivoted to thepower lever for turning movement on an axis which provides a greaterlever ratio for effecting initial movement of the master cylinder pistonupon initial operation of the brake pedal, thus reducing the force whichmust be applied to the brake pedal to initially move the piston. Suchinitial movement of the brake pedal effects operation of the valvemechanism for the booster motor to render the latter operative for thepower actuation of the power lever, and the pivot pin providing theconnection between the pedal lever and the power lever turns about thefixed supporting axis for the power lever, thus providing for thenecessary distance of movement of the master cylinder piston to displacean ample supply of hydraulic fluid for each complete brake application.

While the structure of the copending application discussed above isdefinitely advantageous over prior similar arrangements, it stillrequires the operator to exert against the pedal pad a force greaterthan that which is desirable in the initial operation of the pedallever. This resistance is due to the fact that initial movement of thepedal lever transmits positive movement to the master cylinder piston.

In the other copending application referred to above, Serial No.488,258, the resistance to initial movement of the pedal pad iseliminated'through the use of a rocker interposed between the pedallever and power lever and connected to the push rod for the mastercylinder piston. This rocker is biased to a normal position in which ithas lost motion connection with the pedal lever when the latter is innormal off position, and accordingly the pedal lever is initiallymovable from its off position to move the motor valve mechanism andeffect energization of the motor without transmitting movement to themaster cylinder piston, thus providing an extremely soft pedal. As amatter of fact, the pedal in such mechanism is softer than is desired bymany motor vehicle operators, such operators having the feeling uponinitial operation of the brake pedal that the pedal pads are fallingaway from their feet.

An important object of the present invention is to provide a novelbooster brake mechanism wherein all of the advantages of the structuresof the two copending applications referred to are retained, but whereintoo great a degree of softness in the brake pedal is eliminated byproviding an initial extremely limited, but progressively 2,877,873Patented Mar. 17, 1959 increasing, resistance to the brake pedal as thelatter is moved from its normal ofl? position.

A further object is to provide in combination with a lever mechanism ofthe type referred to above, a booster motor having means thereinresponsive to the degree of energization of the motor for resistingmovement of the brake pedal from normal off position with an initiallyextremely low resistance which progressively increases at least to thepoint where the rocker referred to above comes into operation to reactagainst the brake pedal, thus not only eliminating an excessive degreeof softness in the brake pedal but also preventing the rocker frombecoming too suddenly effective for resisting movement of the brakepedal.

A further object is to provide an improved structure of the characterreferred to wherein the motor structure is improved by utilizing abellows type motor in the drivers compartment of the vehicle and havinga stationary motor head fixed to the fire wall, and by supplying air tothe motor through an air cleaner arranged forwardly of the fire wall,thus silencing the admission of air to the motor and facilitating in anextremely simple manner the maintenance under atmospheric pressure ofone side of the diaphragm which is employed for the progressiveresisting of initial movement of the brake pedal from its normal offposition.

Other objects and advantages of the invention will become apparentduring the course of the following description.

In the drawings I have shown one embodiment of the invention. In thisshowing:

Figure 1 is a side elevation of the apparatus, the fire wall of thevehicle being shown in section and parts of the motor being broken away;

Figure 2 is a rear face view of the apparatus, the sup porting bracketbeing shown in section;

Figure 3 is an enlarged axial sectional view through the motor andassociated elements;

Figure 4 is a section on line 44 of Figure 3; and

Figure 5 is a detail perspective view of the spool valve.

Referring particularly to Figure l, the numeral 10 designates aconventional motor vehicle fire wall forwardly of which is arranged amaster cylinder 11 having a conventional plunger (not shown) operable bya rearwardly extending rod 12. The master cylinder, of course is carriedby the fire wall 10 and such Wall also supports a rearwardly extendingsupporting bracket 13 of generally inverted U section (Figure 2) andcomprising a top wall 14 and opposite parallel side walls 15 and 16.

A bolt 21 extends through the bracket 13 and forms a fixed supportingpivot for a power lever indicated as a whole by the numeral 17. Thislever is of inverted J shape and comprises a relatively long dependingarm 18, a laterally extending preferably integral top portion 19 and ashorter integral depending arm 20 spaced from and parallel to the upperportion of the arm 18.

A pedal lever indicated as a whole by the numeral 22 is provided at itslower end with a conventional pedal pad 23 and has its upper end 24arranged inwardly of and adjacent the upper end of the lever arm 18. Aplate 25, preferably shaped similar to the upper end 24 of the pedallever, is spaced from such portion of the pedal lever and arrangedadjacent the arm 20. The plate 25 and upper lever end 24 are fixed inspaced relation to each other by upper and lower rivets 26 and 27.

A rocker 30 is arranged between the plate 25 and upper lever end 24 andthe latter elements and the rocker 30 are pivotally connected to thepower lever by a pivot pin 31 passing through the power lever arms 18and 20. The rocker 30 is provided with a recess 32 formed as a sectionof a cylinder and receiving a correspondingly shaped head 33 carried bythe push rod 12. The rocker is provided with a depending finger 35normally spaced from the rivet 27 when the parts are in the normal offpositions shown in Figure 1, the rivet 27 serving as a stop for thefinger 35 in a manner to be described. The upper end of the rocker isprovided with a finger 36 normally seating against the pivot pin 21 andengaged by one end of a compression spring 37. The other end of thisspring bears against a bracket 38 welded or otherwise secured at itsupper end to the top portion 19 of the power lever. The spring 37 biasesthe rocker 30 for clockwise turning movement about the pivot pin 31 tothe position shown in Figure 1.

The power lever 17 is operable by a motor indicated as a whole by thenumeral 42. The motor 42 comprises a stationary head 43 (Figure 3) fixedto a stationary depending bracket 44 secured in any suitable manner tothe fire wall 10. The stationary wall 43 is provided with a forwardlyextending annular flange 45 having its forward extremity mounted in anopening 46 in the fire wall and cushioned with respect to the fire wallas at 47.

The motor further comprises a pressure movable head 50 spaced from thefire wall rearwardly thereof. A bellows 51 is connected between themotor heads and is preferably provided with subtending rings 52 toprevent the radial collapsing of the bellows when vacuum is present inthe motor chamber 53 within the bellows.

The motor head 50 carries as an integral part thereof an axial valvehousing 55 having a port 56 communicating with a nipple 57 adapted forconnection with a flexible hose 57' leading to the intake manifold ofthe motor vehicle engine as the preferable source of vacuum foroperating the motor. The valve housing is provided therein with a sleeve58 having an external annular groove 59 in fixed communication with thevacuum port 56, and the sleeve is provided therethrough with radialports 60 communicating with the groove 59. The sleeve 58 is provided inspaced relation to the ports 60 with additional radial ports 61 openinginto a chamber 62 in a rearwardly extending annular flange 64 formedintegral with the motor head 50. This flange is provided with ports 65affording fixed communication between the chamber 62 and the motorchamber 53.

The sleeve 58 is maintained in position by a clip 68 which holds thesleeve 58 in its rearward limit of movement in clamping engagement withthe peripheral portion of a diaphragm 69 for a purpose to be described.

A spool valve 72 is slidable in the sleeve 58 and is provided with anaxial bore 73 communicating through ports 74 with an external groove 75normally communicating with the sleeve ports 61 and movable out ofregistration therewith when the motor is energized. The positions of theparts upon initial energization of the motor are shown in Figure 3.

The sleeve valve is further provided with an external axially elongatedgroove 77 in fixed communication with the port 60 and out ofcommunication with the ports 61, and movable to a position, as in Figure3, connecting the ports 60 and 61.

As further described below, the axial bore 73 is in fixed communicationwith the atmosphere and this bore communicates through port 79 with achamber 80 back of the diaphragm 69, thus maintaining such chamber atatmospheric pressure. A reaction diaphragm 84 has its peripheral portionclamped against the forward edge of the flange 64 by a sheet metal cap85 secured to the flange 64 by screws 86. The inner edge of thediaphragm 84 is fixed to the valve 72 as at 87, and a spring 88 isinterposed between the cap 85 and diaphragm 84 to urge the valve 72rearwardly to its normal motor de-energizing position. It will beapparent that the rear face of the diaphragm 84 is always subject topressure present in the chamber 62. The forward face of the diaphragm isalways subject to atmospheric pressure, in a manner to be described, inthe chamber 90, formed in the cap 85. An axial tube 92 is welded orotherwise secured at its rear end to a cylindrical flange 93 carried bythe cap 85. The tube 92 extends through the stationary motor wall 43 andsuch wall is provided with a deformable double-lipped seal 94 backed uppreferably by a rawhide or other deformable seal 95, these sealspermitting the tube 92 to alter its position axially of the head 43during operation of the motor, as will become apparent.

Forwardly ,of the fire wall 10, the tube 92 carries 21 preferablystamped casing 98 to which is secured a bumper 99 engageable with theforward end of the flange 45. This bumper, as will become apparent,limits rearward movement of the tube 92 and the elements connectedthereto, and silences the arresting of the parts in such normalpositions. The casing 98 houses an air cleaner 100 and is provided witha cap 101 apertured as at 102 for the admission of air into the aircleaner. A heavy return spring 104 engages at opposite ends with themotor heads 43 and 50 to urge the head 50 and tube 92 to the normal otfpositions referred to.

The valve housing 55 is provided with a rearwardly extending ear 105pivotally connected by a bolt 106 to the lower end of the power leverarm 18. This pin also extends through a slot 107 formed in the pedallever 22 to provide lost motion connection between the pedal lever andthe pin 106. The left-hand side of the slot 107, in the off positions ofthe parts shownin Figure 1, engages the pin 106, and the pedal lever ismovable an appreciable distance from its normal off positionindependently of the pin 106. The pedal lever 22 carries a disk 109through which the slot 107 extends, and this disk is provided with apreferably integral lateral extension 110 extending across andengageable with the central portion 111 of the diaphragm 69, suchportion of the diaphragm covering a projecting button 112 formedintegral with the valve 72. Such central portion 111 of the diaphragmsilences engagement of the projection 110 with the valve, and suchprojection is operative for moving the valve to energize the motor uponoperation of the brake pedal.

Operation The. parts normally occupy the positions shown in Figure 1,the valve groove 77 being moved to the right (Figure 1) of the ports 61and these ports being open to the atmosphere through the valve ports 74,tube 92 and air cleaner 100. Accordingly, atmospheric pressure will bepresent in the motor chamber 53. At the same time, the upper finger 36of the rocker 30 will be in engagement with the pivot pin 21, while thelower finger 35 will be spaced to the left of the rivet 27.

The brakes are applied in the usual manner through operation of theoperators foot on the pedal pad 23. The pedal lever 22 is pivoted on thepin 31 carried by the power lever 17. When the pedal lever is initiallyoperated, therefore, such lever will turn about the axis of the pin 31and the transverse member 110 will move the valve 72 to the left asviewed in Figures 1 and 3. This operation moves the valve groove 75 outof registration with the ports 61 and moves the groove 77 to a positioncracking the ports 61 to the vacuum chamber 56. The chamber 53 of themotor will now be cut off from the atmosphere and will be connected tothe source of vacuum, whereupon atmospheric pressure moves the head 50of the motor toward the left. This movement of the motor head 50 istransmitted to the power lever through the pin 106 and this lever willnow start to turn about the axis of its supporting pin 21.

When the parts were in their off positions, atmospheric pressure willhave existed in both diaphragm chambers 62 and 90, and the only forcetending to move the valve 72 to its off position will have been theforce of the light return spring 88. Initial movement of the pedallever, therefore, takes place solely against the loading of the lightspring 88 and the pedal lever will turn about the axis of the pin 31,this pin momentarily remaining stationary. As soon as the sleeve ports61 are cracked to the vacuum chamber 56, however, differential pressureswill be set up on opposite sides of the diaphragm 84 and movement of thevalve 72 will be resisted by the tension of the light spring 88 plus thedifferential pressures aifecting the diaphragm 84, such differentialpressure initially being light and progressively increasing as air isevacuated from the chamber 62 and the motor chamber 53.

It will be apparent, therefore, that only the very first increment ofmovement of the brake pedal will be resisted solely by the spring 88 andany feeling that the brake pedal is falling away from the operators footwill be promptly prevented by the initial establishment of differentialpressures in the diaphragm chambers 62 and 90. In this connection it ispointed out that it is highly desirable to eliminate the necessity forthe operators having to move the master cylinder plunger through theeffort of foot pressure since it requires appreciable force on the partof the operator. With prior constructions, this necessity for displacingfluid by the effort of the operators foot caused a lumpiness in thebrake operation which is eliminated by the lever mechanism shown in thecopending application of Jeannot G. Ingres, Serial No. 488,258, referredto above. The present construction utilizes the rocker 30 similar to therocker of the copending application just referred to, and the lostmotion between the finger 35 and pin 27 permits initial movement of thebrake pedal without transmitting movement to the master cylinderplunger. The prior construction is objectionable to many operators,however, because of the almost total absence of any resistance to pedallever movement in the initial stages of brake operation.

The disadvantage referred to is overcome in the present constructionsince the differential pressures affecting the diaphragm 84 come intoplay prior to engagement of the finger 35 with the pin 27, as furtherreferred to below, and accordingly the operator in the initial stages ofbrake operation will encounter increasing resistance to pedal movement.This resistance, of course, is progressive without providing anylumpiness, and the pedal lever accordingly is provided with a highlydesirable softness without being too freely operable. In the structureof the copending application just referred to, the initial stages ofbrake pedal lever movement take place against negligible resistance asstated, until play is taken up between the rocker corresponding to therocker 30 and the pedal lever, whereupon the operator feels anappreciable increase in pedal resistance. The same resistance isencountered in the present construction upon engagement of the finger 36with the rivet 27. However, the increase in pedal resistance is notsudden since the progressive building-up of the resistance due to thereaction of the diaphragm 84 reaches the point where engagement betweenthe finger 35 and rivet 27 is hardly noticed. Thus the diaphragmreaction acts in combination with the rocker 30 to provide a smoothprogressive resistance which is highly desirable.

As previously stated, energization of the motor moves the head 50 whichtransmits movement through the ear 105 and pin 106 to the power lever17. As soon as this lever starts to move about the axis of itssupporting pin 21, the pin 31 will partake of similar movement since itis carried by the power lever. With the rocker 30 remaining for the timebeing in a position with its finger 36 engaging the pin 21 so that therocker moves bodily with the power lever, force will be applied throughthe head 33 to the rod 12 to efiect movement of the master cylinderplunger. The spring 37 is so tensioned as to prevent counterclockwiseturning movement of the rocker 30 when the latter initially impartsmovement to the rod 12. The spring 37 may be so designed as to beovercome by any desired reaction pressure in the master cylinder, andwhen such pressure is reached, the reaction forces acting through therod 12 and head 33 will start to turn the rocker counterclockwise aboutits pivot pin 31, against the tension of the spring 37. This operationmoves the finger 35 into engagement with the rivet 27; Thereafter, theoperator will apply force to the rocker 30 through the rivet 27, whilethe power lever will apply force to the rocker through the pivot pin 31.These two forces combine to effect movement of the master cylinderpiston, as will be apparent.

The foregoing operations in applying the brakes take place with the pin106 arranged out of contact with the right-hand edge of the slot 107. Asthe brake pedal is initially operated to energize the motor, theleft-hand side of the slot 107 moves away from the pin 106 and this pinwill remain out of engagement with both sides of the slot 107 up to thepoint of power run-out in the motor, that is, the point at which themotor is energized to its maximum extent. This point occurs prior to thepoint of maximum brake application. Beyond the point of power run-out,the right-hand side of the slot 107 will move into engagement with thepin 106, and further application of foot pressure against the pedal pad23 will cause the pedal lever 22 to assist the motor in transmittingforces to the power lever through the pin 106.

The brakes are released by releasing the pedal lever in the usualmanner, whereupon the spring 88, assisted by the ever existingatmospheric pressure in the chamber 90, will return the valve 72 to itsnormal off position. The motor chamber 53 will again be connected to theatmosphere through ports 74 and through the tube 92 and air cleaner 100.The usual return spring (not shown) in the master cylinder will returnthe power lever to its normal off position, and as soon as the reactionfrom the master cylinder against the rocker 30 diminishes to the properpoint, the spring 37 will return the rocker 30 to the normal offposition shown in Figure 1. The return spring 104 in the motor returnsthe head 50 to its off position and movement of such head to offposition is limited by the bumper 99 carried by and forming in efiect apart of the air cleaner housing 98. This bumper being of resilientmaterial also silences contact between the parts when the off positionreferred to is reached.

The tube 92 permits the air cleaner to be arranged forwardly of the firewall 10, thus silencing the rush of air into the motor when the brakesare released. The tube 92, being fixed with respect to the motor head 50and valve housing 55 and associated elements, maintains the properposition of the motor head against sagging to a position with its axissloping downwardly toward the head 43. Such sagging otherwise would bepermitted because of the flexibility of the bellows 51.

From the foregoing it will be apparent that the present inventioneliminates the lumpy operation occurring in a mechanism of this kindwhere it is necessary for the operator, through pressure on the pedalpad to initiate movement of the master cylinder plunger. It also will beapparent that such lumpiness is eliminated through the use of the rocker30 which is relatively independently movable with respect to the pedallever during initial operation thereof. Such advantageous use of therocker 30, however, has the disadvantage stated above of providinginsufficient resistance to initial movement of the brake pedal up to thepoint where the finger 35 contacts the rivet 27, at which point pedalresistances increase rather abruptly. With the present construction,during movement of the brake pedal from its fully off position up to thepoint where engagement of the finger 35 with the rivet 27 takes place, aprogressively increasing elastic fluid pressure resistance reactsagainst the brake pedal, thus eliminating the unpleasant feeling thatthe pedal is falling away from the foot. At the same time, thisprogressively increasing resistance is not excessive and may be designedto provide any desired degree of resistance in accordance with the areaof the diaphragm 84. Moreover, since the elastic fluid pressureresistance increases progressively, the point of contact of the finger35 with the rivet 27 is unnoticed in the operation of the brake pedalinstead of providing a highly objectionable sudden increase in reaction.

It is to be understood that the form of the invention herewith shown anddescribed is to be taken as a preferred example of the same and thatsuch changes in the shape, size and arrangement of parts may be made asdo not depart from the spirit of the invention or the scope of theappended claims.

I claim:

1. A force producing device for actuating an operable member, comprisinga fluid pressure motor, a power transmitting member connected to saidmotor to be actuated thereby, an operator operated member connected tosaid power transmitting member, a delayed action force transmittingelement connected to said power transmitting member and said operatoroperated member and engaging said operable member, said operatoroperated member having a normal ofi position and said delayed actionelement having a normal position in which it has lost motion connectionwith said operator operated member for predetermined movement of saiddelayed action element from its normal position before engaging saidoperator operated member, biasing means between said power transmittingmember and said delayed action element tending to hold the latter in itsnormal position, a valve mechanism connected to said motor and to saidoperator operated member and having fluid connection with a source ofpressure different from the atmosphere and operable by said operatoroperated member in initial movement thereof from its oil? position toenergize said motor, and reaction means connected to be operable byenergization of said motor for progressively resisting movement ofsaid'operator operated member throughout movement thereof from itsnormal otf position, said biasing means being of sufiicient strength toeffect movement of said operable member during initial energization ofsaid motor until resistance to movement of said operable memberincreases to a predetermined point, whereupon said lost motionconnection will be taken up and reaction will be directly transmittedfrom said operable member through said delayed action element to saidoperator operated member.

2. A force producing device for actuating an operable member, comprisinga fluid pressure motor, a power lever connected to said motor andpivoted for turning movement on a fixed axis, a pedal lever pivoted tosaid power lever on a second axis spaced from said fixed axis andmovable with said power lever, a valve mechanism connected to said motorand to said pedal lever and having fluid connection with a source ofpressure different from the atmosphere and operable by said pedal leverin initial movement thereof from a normal of? position to energize saidmotor, a delayed action force transmitting element connected to saidpower lever and connected to said operable member, means biasing saiddelayed action element to a normal position in which it has lost motionrelative to said pedal lever when the latter is in its normal offposition whereby said delayed action element is movable from its normalposition through a predetermined angle of turning movement beforeengaging said pedal lever, and means connected to be responsive toenergization of said motor for progressively opposing movement of saidpedal lever from said normal off position, said biasing means being ofsufficient strength to effect movement of said operable member duringinitial energization of said motor until resistance to movement of saidoperable member increases to a predetermined point, whereupon said lostmotion will be taken up and reaction will be directly transmitted fromsaid operable member through said delayed action element to said pedallever.

3. A force producing device for actuating an operable member, comprisinga fluid pressure motor having a pressure movable head one side of whichis open to the atmosphere and at the other side of which is a variablepressure chamber, a valve mechanism connected to said motor and havingfluid connection with a source of vacuum and operable for connectingsaid chamber to said source, a power lever mounted for turning movementon a fixed axis and connected at a point spaced from such axis with saidmovable motor head, a pivot pin carried by said power lever between saidfixed axis and said motor, a pedal lever connected to said pivot pin andhaving connection with said valve mechanism for operating the latterupon movement of said pedal lever from a normal off position, a rockermounted on said pivot pin and having mechanical connection with saidoperable member between said pivot pin and said motor, means biasingsaid rocker to a normal position in which it has lost motion connectionwith said pedal lever when the latter is in its normal position wherebysaid rocker is movable from its normal position through a predeterminedangle of turning movement about said pivot pin independently of saidpedal lever, and reaction means connected to be subject to energizationof said motor to increasingly oppose movement of said pedal lever fromits normal off position, said biasing means being of sufficient strengthto eifect movement of said operable member during initial energizationof said motor until resistance to movement of said operable memberincreases to a predetermined point, whereupon said lost motionconnection will be taken up and reaction will be directly transmittedfrom said operable member through said rocker to said pedal lever.

4. A force producing device for actuating an operable member, comprisinga fluid pressure motor having a stationary head, a movable head spacedtherefrom, and a bellows connecting said heads and defining therewith avariable pressure chamber, a valve mechanism carried by said movablehead and having fluid connection with a source of vacuum and beingarranged to control connection of said variable pressure chamber to theatmosphere and said source, a power transmitting member connected tosaid movable head, an operator operated member connected to said forcetransmitting member, a delayed action force transmitting elementconnected to said power transmitting member and engaging said operablemember, said delayed action element having a normal position in which ithas lost motion connection with said operator operated member when thelatter is in a normal off position whereby said force transmittingelement is movable in a predetermined range of movement from its normalposition to a point where it engages said operator operated member,biasing means between said power transmitting member and said delayedaction element tending to hold the latter in its normal position, saidoperator operated member being connected to said valve mechanism tooperate the latter and initiate communication between said motor chamberand said source at the beginning of said range of movement, and reactionmeans having mechanical connection with said operator operated memberand connected to be operable by a drop in pressure in said motor chamberfor increasingly resl stmg movement of said operator operated member,said biasing means being of sufficient strength to effect movement ofsaid operable member during initial energization of said motor untilresistance to movement of said operable member increases to apredetermined point, whereupon said lost motion connection will be takenup and reaction will be directly transmitted from said operable memberthrough said force transmitting element to said operator operatedmember.

5. A force producing device for actuating an operable member, comprisinga fluid pressure motor having a stationary head, a movable head spacedtherefrom and a bellows connecting said heads and forming therewith avariable pressure motor chamber, a valve mechanism carried by saidmovable head and having fluid connection with a source of vacuum andsaid motor chamber, a power lever connected to said movable head, apedal lever connected to said power lever and having mechanicalengagement with said valve mechanism to operate the latter and connectsaid chamber to said source upon movement of said pedal lever from anormal 011? position, a delayed action force transmitting elementmovably supported with respect to both of said levers and connected tosaid operable member, means biasing said delayed action element to anormal position in which it has lost motion connection with said pedallever when the latter is in its normal olf position whereby said delayedaction element is movable from its normal position independently of saidpedal lever through a predetermined range of movement, and a reactiondiaphragm connected between said movable head and said valve mechanism,said diaphragm having one face exposed to the atmosphere 15 and itsother face exposed to pressure in said motor chamber to react againstsaid pedal lever immediately upon initial energization of said motor,said biasing means being of sutficient strength to effect movement ofsaid operable member during initial energization of said motor untilresistance to movement of said operable member increases to apredetermined point, whereupon said lost motion connection will be takenup and reaction Will be directly transmitted from said operable memberthrough 10 said delayed action element to said pedal lever.

References Cited in the file of this patent UNITED STATES PATENTS1,878,944 Lombard Sept. 20, 1932

